Conventionally, two types of devices, namely thermionic and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction type emission devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
A known example of the surface-conduction type emission devices is described in, e.g., M. I. Elinson, “Radio E-ng. Electron Phys., 10, 1290 (1965) and other examples will be described later.
The surface-conduction type emission device utilizes the phenomenon that electrons are emitted by a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction type emission device includes electron-emitting devices using an Au thin film (G. Dittmer, “Thin Solid Films”, 9,317 (1972)), an In2O3/SnO2 thin film (M. Hartwell and C. G. Fonstad, “IEEE Trans. ED Conf.”, 519 (1975)), a carbon thin film (Hisashi Araki et al., “Vacuum”, Vol. 26, No. 1, p. 22 (1983)), and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 11 is a plan view showing the device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction type emission devices. Referring to FIG. 11, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering.
This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 11. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 11 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction type emission devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In forming processing, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after forming processing, electrons are emitted near the fissure.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, “Field Emission”, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, “Physical Properties of Thin-Film Field Emission Cathodes with Molybdenium Cones”, J. Appl. Phys., 47, 5248 (1976).
FIG. 12 is a sectional view showing the device by C. A. Spindt et al. described above as a typical example of the FE type device structure. In FIG. 12, reference numeral 3010 denotes a substrate; 3011, an emitter wiring made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, a gate electrode. In this device, a voltage is applied between the emitter cone 3012 and gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012.
As another FE type device structure, there is an example in which an emitter and gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of FIG. 12.
A known example of the MIM type electron-emitting devices is described in C. A. Mead, “Operation of Tunnel-Emission Devices”, J. Appl. Phys., 32,646 (1961). FIG. 13 shows a typical example of the MIM type device structure. In FIG. 13, reference numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 100 Å; and 3023, an upper electrode made of a metal and having a thickness of about 80 to 300 Å. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper and lower electrodes 3023 and 3021 to emit electrons from the surface of the upper electrode 3023.
Since the above-described cold cathode devices can emit electrons at a temperature lower than that for thermionic cathode devices, they do not require any heater. The cold cathode device has a structure simpler than that of the thermionic cathode device and can shrink in feature size. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the thermionic cathode device is low because the thermionic cathode device operates upon heating by a heater.
For this reason, applications of the cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the surface-conduction type emission devices have a simple structure and can be easily manufactured, and thus many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the assignee of the present application, a method of arranging and driving a lot of devices has been studied.
Regarding applications of the surface-conduction type emission devices to, e.g., image forming apparatuses such as an image display apparatus and image recording apparatus, charge beam sources, and the like have been studied.
Particularly, as an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the assignee of the present application, an image display apparatus using a combination of a surface-conduction type emission device and a fluorescent substance which emits light upon irradiation of an electron beam has been studied. This type of image display apparatus using a combination of the surface-conduction type emission device and fluorescent substance is expected to exhibit more excellent characteristics than other conventional image display apparatuses. For example, compared with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require any backlight because it is of a self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the assignee of the present application. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat panel display reported by R. Meyer et al. (R. Meyer:“Recent Development on Microtips Display at LETI”, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)).
An application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the assignee of the present application.